Paypal latest CheckoutNETSDK - get 'invalid_client'

Paypal latest CheckoutNETSDK - get 'invalid_client'

My MERCHANT_ID is: 58V2NEF27DY7E

I downloaded the latest CheckoutNETSDK and replaced environment() method body with my Sandbox client_id and secret obtained directly from my PayPal developer account page so that it didn't get them from the environment. I also refreshed the secret several times.